Basic doubt on AMS-designer and co-simulation

Hi,

I'm new with AMS designer.
I've few basic questions:

1. Could anyone please explain me the differences between co-simulation and AMSDesigner-with ultrasim simulation (AMS-Ultra)?
2. Does ultrasim support simulating RTL verilog codes?
3. How the Mixed Signal circuit gets simulated with AMS designer?


Thank you.

Kind regards.